JP2002103444A - Biaxially oriented polyester film and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide a biaxially oriented polyester film high in anisotropy and excellent in tearing rectilinear propagation while dynamical properties, smell preserving properties, heat resistance, oil resistance, low hygroscopicity, and especially dimensional stability in a dry-heated or wet-heated environment required for a food packaging material, which are the features of the polyester film, are kept. SOLUTION: The biaxially oriented polyester film having phase separation structure and an anisotropy evaluation value of 0.70 or below which is a polyester film formed from a mixture comprising at least two polyesters is obtained by a resin melting/extruding process in which a shear rate is increased sharply in terms of a space or in terms of time and a succeeding orientation process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a confectionery, pickle, miso, soup, jam, frozen, refrigerated, retort pouch, etc., having excellent tear straightness, excellent strength, heat resistance and dimensional stability. The present invention relates to a film useful as a packaging material for foods, pharmaceuticals, daily necessities, cosmetics, and the like.

[0002]

2. Description of the Related Art In the packaging of foods, medicines and miscellaneous goods, packaging bags using various plastic films are often used. Two or three layers of a biaxially stretched plastic film and a heat-sealable non-oriented plastic film are used. The packaging bags laminated as described above are widely used. The biaxially stretched polyester film has excellent durability, moisture resistance, mechanical strength, heat resistance and oil resistance, and is manufactured using the tubular method, flat simultaneous biaxial stretching method, flat sequential biaxial stretching method, etc. The biaxially stretched polyester film is widely used in the field of food packaging.

[0003] However, a packaging bag using a biaxially stretched polyester film has a problem that tear-openability is poor. There is a method of providing a notch to improve the openability, but when tearing from the notch, a phenomenon that it does not tear linearly often occurs, and not only is the content scattered but wasted, but also cookies etc. The soft confectionery may break when opened, or may cause troubles such as soiling clothes when the contents are liquid.

As an easy-opening packaging material having excellent straightness when the film is torn, there is a material obtained by laminating a uniaxially stretched polyolefin film as an intermediate layer. Examples of such a film include a three-layer laminated film of a biaxially oriented polyester film / a uniaxially oriented polyolefin film / an unoriented polyolefin film,
An intermediate layer had to be provided, which was problematic in terms of cost, and its use was limited.

In order to solve such a problem, a polyester film having a single layer and excellent tear straightness has been devised. Such a polyester film expresses tear straightness utilizing the anisotropy of the phase separation structure of the polymer blend. In order to control the anisotropy of this film,
For example, JP-A-08-169962 defines anisotropy in an unstretched sheet. However, even when using a specific resin composition and using such extrusion conditions, it has been difficult to reliably control the anisotropy stably. In addition, since the film must be stretched, relaxed, heat-set, etc. before the film is completed, the anisotropy changes depending on the subsequent experience, so that the final desired anisotropy should be controlled. Was difficult.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such a problem, and it is intended to solve the problems of the mechanical properties, fragrance retention, heat resistance, oil resistance and low mechanical properties which are characteristic of biaxially stretched polyester films. To stably provide a biaxially stretched polyester film having high anisotropy and excellent tear straightness while maintaining moisture absorption and dimensional stability under dry heat and wet heat environments required especially for food packaging materials. Is what you do.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve such problems, and as a result, have reached the present invention. That is, the biaxially oriented polyester film of the present invention is a polyester film composed of a mixture of two or more polyesters, and a resin melt extrusion step of rapidly increasing the shear rate spatially and / or temporally, followed by a resin melt extrusion step. Having a phase separation structure obtained by a stretching step,
In addition, the isotropic evaluation value is 0.70 or less. In this case, the biaxially oriented polyester film preferably has excellent tearing straightness in the machine flow direction. In this case, it is preferable that the layer separation structure has a string-like island shape. Furthermore, in this case, the mixture of the above polyester is a crystalline polyester resin (A) containing 80 mol% or more of terephthalic acid (A) at 90 to 70 wt%, a crystal segment having a melting point of 170 ° C. or more, a melting point or softening point of 100 ° C. or less, and a molecular weight of Is 40
The mixture is preferably a mixture of 10 to 30% by weight of a block copolymer polyester (B) composed of 0 to 8000 soft polymers. Furthermore, in this case, the mixture of the polyester is a crystalline polyester resin (A) containing at least 80 mol% of terephthalic acid, and has a crystal segment having a melting point of 170 ° C. or more and a melting point or softening point of 100 ° C. or less;
It is a mixture of a block copolymer polyester (B) consisting of a soft polymer having a molecular weight of 400 to 8000 and polybutylene terephthalate (C), and (A) is 90 to 70 wt.
%, And the total amount of (B) and (C) is preferably 10 to 30 wt%. Furthermore, in this case, it is preferable that the biaxially oriented polyester film is obtained by a resin melt extrusion step in which the shear rate is sharply increased spatially and / or temporally, and a subsequent stretching step. Furthermore, in this case, a method for producing a biaxially oriented polyester film, which comprises a resin melt extrusion step of rapidly increasing the shear rate spatially and / or temporally and a subsequent stretching step, is preferred. is there.

DETAILED DESCRIPTION OF THE INVENTION The crystalline polyester (A) of the present invention contains terephthalic acid in an amount of 80 mol% or more.
Polyester with ethylene terephthalate as the main repeating unit, polyethylene terephthalate (PE
T) is optimal, but a copolymer of PET and polybutylene terephthalate (PBT), PET and polyethylene naphthalate (PEN), or a mixture thereof can be used.

The polyester has an intrinsic viscosity of 0.6.
It is preferably at least 0 dl / g, more preferably at least 0.62 dl / g and at most 0.90 dl / g. When the one having an intrinsic viscosity of less than 0.62 dl / g is used, both impact strength and tear straightness are not excellent. If the intrinsic viscosity is more than 0.90 dl / g, the extrusion moldability is poor. The method for polymerizing the crystalline polyester (A) is not particularly limited, but a solid-phase polymerization method can be used in combination to keep the intrinsic viscosity in a suitable range.

In the block copolymer polyester (B) of the present invention, the crystal segment having a melting point of 170 ° C. or more has a melting point of 170 ° C.
° C or higher, for example, residues of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and ethylene glycol, propylene glycol, butanediol, pentamethylene glycol, and P-xylene glycol And polyesters comprising residues of aliphatic, aromatic and alicyclic diols such as cyclohexanedimethanol, etc., and it is particularly desirable that terephthalic acid residues account for 80 mol% or more.

A soft polymer having a molecular weight of 400 to 8000 has a melting point or softening point of 100 ° C. or lower when measured only with the above-mentioned segment constituents. When the one having a molecular weight of 400 or less is used, the obtained block copolymerized polyester has a low melting point and a high tackiness, which makes it difficult to process the compounded film. In addition, the molecular weight is 80
If it exceeds 00, the soft polymer undergoes layer separation, exhibits an extremely high melt viscosity, becomes hard and brittle, and becomes difficult to remove from the polymerization vessel after the copolymerization reaction. When used for molding, the transparency is poor or unfavorable. Preferably it has a molecular weight of 800 to 1200.

The ratio of the low melting point soft polymer in the block copolymerized polyester is preferably in the range of 1 to 12 mol%. When the amount is less than 1 mol%, the properties as a soft polymer cannot be obtained. When the amount exceeds 12 mol%, the dispersion of the block copolymerized polyester (B) becomes large at the time of mixing and melting with the crystalline polyester (A), and the tearing straightness is reduced. It cannot be obtained, and the transparency deteriorates. Further, the range is preferably 3 to 8 mol%, and particularly preferably the range is 2 to 4 mol%.

Examples of such a low melting point soft polymer include polyethylene oxide glycol, polytetramethylene oxide glycol, polypropylene oxide glycol, copolymerized glycol of ethylene oxide and propylene oxide, and copolymerized glycol of ethylene oxide and tetrahydrofuran. Examples thereof include aliphatic polyesters such as polyether, polyneopentyl azelate, polyneopentyl adipate, and polyneopentyl sepate, and polylactones such as poly-ε-caprolactone and polypivalolactone. Preferably, polyethylene oxide glycol, polytetramethylene oxide glycol and the like are practical. These block copolymerized polyesters can be produced by a usual condensation polymerization method.

Specific examples of the block copolymer polyester used in the present invention include polyethylene terephthalate-polyethylene oxide block copolymer, polyethylene terephthalate-polytetramethylene oxide block copolymer, and polybutylene terephthalate-polyethylene oxide block copolymer. , Polybutylene terephthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-polyethylene oxide, polypropylene oxide block copolymer, polytetramethylene terephthalate / isophthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-poly-ε -Caprolactone block copolymer, polyethylene terephthalate-polyneopentyl Block copolymer of polyester from di (4-carboxyphenoxy) ethane and ethylene glycol and block copolymer of polyethylene glycol, polyester from bis (N-paracarboethoxyphenyl) adipamide and ethylene glycol Examples include block copolymers with polyethylene glycol.

In the present invention, the crystalline polyester (A)
It is necessary to mix the block copolymer polyester (B) with the crystalline polyester (A) in a proportion of 90 to 70 wt% and the block copolymer polyester (B) in a proportion of 10 to 30 wt%. Is 90 to 75% by weight of the crystalline polyester (A), 10 to 25% by weight of the block copolymerized polyester (B), more preferably 90 to 80% by weight of the crystalline polyester (A) and 10 to 20% by weight of the block copolymerized polyester (B). is there. If the amount of the block copolymer polyester (B) is less than 10% by weight, tearing straightness cannot be obtained. Also, a block copolymerized polyester (B)
If it exceeds 30% by weight, the tensile strength of the biaxially stretched polyester film is reduced, the dimensional stability and the rigidity are reduced, and the polyester film cannot be used.

A part of the mixture of the block copolymerized polyester (B) may be replaced with polybutylene terephthalate.

The heat shrinkage of the biaxially stretched polyester film of the present invention is preferably 3% or less in both the machine flow direction (MD direction) and the width direction (TD direction) at 150 ° C. for 30 minutes. When the heat shrinkage exceeds 3%, printability deteriorates, which is not preferable.

The isotropic evaluation value of the biaxially stretched film of the present invention is preferably 0.70 or less, and 0.60 or less.
The following is more preferred. Further, when it was 0.30 or less, the warp width when the polyester (B) was torn by 200 mm when the polyester (B) was 19 wt% was about ± 1 mm. Isotropic evaluation value of 0.7
If it exceeds 0, tearing straightness in the machine flow direction cannot be obtained.

As a method for reducing the isotropic evaluation value of the film to 0.70 or less, a step of sharply increasing the spatial and / or temporal shear rate in the resin melt extrusion step is further provided. It is effective to provide a process near the point where extrusion is completed. This makes it possible to stably form the features or traces of the stringing island phase separation structure generated. Further, using the polyester composition described above, for example, increasing the polyester (B), stretching by biaxial stretching, and setting the temperature of heat setting to a higher range,
Etc. were also found to be effective.

As a method for producing the film of the present invention, for example, a crystalline polyester (A) and a block copolymerized polyester (B), or a mixture thereof mixed with polybutylene terephthalate in the form of chips is charged into an extruder. After being heated and melted, it is extruded and discharged in a sheet form from a die orifice of a T-die.

In order to provide a step of sharply increasing the spatial and / or temporal shear rate near the time when the resin melt extrusion is completed, for example, the sheeting profile may be steep or stepwise. Using a die with a reduced lip, narrowing the molten pipeline near the die entrance sharply and sufficiently from the previous pipe diameter, providing a filter near the die, etc. It is desirable. At this time, the shear rate of the resin at the die orifice was 200 sec.
^From the viewpoint of the above-mentioned effect, it is preferable that the value is ^-1 or more. Further, 300 sec ^-1 or more is preferable.

Next, the sheet in the softened state is closely wound around a cooling drum and cooled. Subsequently, the obtained unstretched sheet is stretched at a stretching ratio of 3 to 4 times in the machine direction at a temperature of 90 to 110 ° C. Then 80 ~ 11
The film is stretched in the transverse direction at a temperature of 0 ° C. at a stretch ratio of 3.5 to 4.5 times. When the stretching ratio is lower than the respective temperatures, a uniform stretched film may not be obtained. On the other hand, when the respective stretching temperatures exceed the respective temperatures, crystallization of the crystalline polyester (A) is promoted, resulting in poor transparency. May be. The biaxially stretched film is subsequently
Heat treatment is performed at a temperature of 0 ° C. If the heat treatment temperature is lower than 210 ° C., the shrinkage of the film increases, which causes deformation when used as a bag. On the other hand, when the temperature is higher than 250 ° C., the film melts and it becomes difficult to form a film.

The biaxial stretching method is not particularly limited, but is preferably a sequential biaxial method using a roll and a tenter. In producing the film of the present invention, there is no problem even if appropriate additives such as an antioxidant, an anti-blocking agent, an ultraviolet absorber, a lubricant and a compatibilizer are added in advance. The biaxially stretched film of the present invention can be subjected to a corona discharge treatment, a flame treatment, a surface hardening treatment, or a surface treatment with various coatings.

[0024]

Next, the present invention will be described specifically with reference to examples. In addition, the measuring method of an Example and a comparative example is as follows.

(Measurement method) Reduced viscosity and intrinsic viscosity Using an Ubbelohde type viscosity tube, a sample was dissolved at a solution concentration of 0.4 g / dl in a mixed solvent of phenol / tetrachloroethane at a weight ratio of 6/4, and reduced from the value measured at a temperature of 30 ° C. The viscosity is determined and, if necessary, converted to the intrinsic viscosity.

Tear straightness: From biaxially stretched film, M
A rectangular film piece having a length of 200 mm in the direction D and a length of 40 mm in the TD direction is cut out, and ten samples having a cutout having a length of 5 mm in the center of one short side of the film piece are prepared.
Next, tear by hand in the MD direction from the incision, ◎ when the propagation edge reached within 2 mm from the center of the short side facing the side where the incision was made, and ○ when it reached within 2 to 5 mm, 5 mm Those that arrived above were marked with △, and those that did not reach the opposite short sides were marked with x. FIG. 1 shows a conceptual diagram.

2. Isotropic evaluation Portable photoelectric colorimeter (COLOR, manufactured by Shibata Chemical Instruments Co., Ltd.)
Using IMETER MODEL C-2), remove the sample holder and disconnect the input line of the photodiode for light reception. The sensor surface of the blue-sensitive photodiode for visible light (BS120) has an elevation angle of 60 degrees from the center of the entrance aperture of the 5 mmφ colorimeter to the exit side of the entrance optical axis.
Attach it at a distance of 21 mm and connect its signal output after disconnecting the photodiode input of the colorimeter. After the leakage is completely removed, the measurement is started. With the incident light (white light) blocked, adjust the meter to 0% with the zero adjustment dial. On a 5 mmφ incident light stop of a colorimeter, 1 to 10 sample films (2 to 5 standard films) are fixed with their cutout directions aligned and stacked. At this time, the MD direction of the sample film is perpendicular to a plane including the optical axis and the center of the sensor. Apply incident light and adjust 100% of the meter with a 100% adjustment dial. Next, the sample film is turned 90 degrees about the incident light stop so that the TD direction of the sample film is perpendicular to a plane including the optical axis and the center of the sensor, and the meter is read (a%). Turn the film 90 degrees in the same direction, adjust the film to 100%, and read the a% reading of 5%.
Repeat several times. Finally, the film is removed and the meter is read with incident light (B%). A% is the average of five a% readings
Then, the isotropic evaluation value I is represented by the following equation (1). I = (AB) / (100-B)

As the anisotropy increases, I takes a value closer to 0.
I takes a value closer to 1 as the anisotropy is smaller. When this evaluation method is performed, the selection of the device is not limited to the above as long as it is optically equivalent and has similar sensitivity.

3. Evaluation of Phase Separation Structure A film sample was cut out and embedded in an epoxy resin in order to form a section of MD and TD sections. This was trimmed and surfaced and then stained in RuO4 vapor for 16 hours. From each stained block, MD, T
An ultrathin section having a D cross section was prepared, meshed, and subjected to carbon vapor deposition to obtain an observation sample. Observation is made by JEOL JE
Acceleration voltage 200k with M-2010 transmission electron microscope
V, observation and photography were directly performed at a magnification of 10,000 times.
When five or more phase separation structures having a length of 500 nm or more were found in a 10 μm square section of the MD cross section, it was judged that there was a stringing island phase separation structure.

Example 1 As a crystalline polyester (A), RE553 manufactured by Toyobo Co., Ltd. (intrinsic viscosity: 0.63 dl / g)
Using, as a block copolymerized polyester (B),
100 mol% of terephthalic acid as a dicarboxylic acid component, 96.7 mol% of butanediol as a diol component, 3.3 mol of polytetramethylene glycol (molecular weight 1000)
1% of a polyester (reduced viscosity of 1.33 dl / g) was mixed at a ratio of 88/15 wt%. This was passed through a filter at a resin temperature of 280 ° C. using a 90 mmφ extruder, and was melt-extruded from a T-die in which the entrance diameter to the die portion was 10 mmφ and the lip exit was stepwise reduced from 2 mm to 1 mm, and the temperature was raised to 25 ° C It was closely cooled to the temperature-controlled cast roll and rapidly cooled to obtain an unstretched sheet having a thickness of about 200 μm. The shear rate at the lip tip at this time was about 500 sec-1.

Then, the obtained unstretched sheet is stretched 3.7 times at 100 ° C. by a roll type longitudinal stretching machine and 4.5 times at 105 ° C. by a tenter type transverse stretching machine, and then heat-treated at 240 ° C. After cooling to room temperature, a biaxially stretched film having a thickness of 12 μm was obtained. The obtained biaxially stretched film was evaluated for isotropy and measured for straightness to tear, and the results are shown in Table 1.

(Example 2) The unstretched sheet obtained in the same manner as in Example 1 was stretched 4.5 times at 105 ° C with a tenter-type transverse stretching machine and at 100 ° C with a roll-type longitudinal stretching machine. After stretching 3.7 times, the film was heat-treated at 240 ° C. and cooled to room temperature to obtain a biaxially stretched film having a thickness of 12 μm.

(Comparative Example 1) In Example 1, biaxial stretching was carried out in the same process as in Example 1 except that the melt extrusion was carried out from a T-die in which the entrance diameter to the die portion was 30 mmφ and the lip exit was kept at 2 mm. A film was obtained.

(Comparative Example 2) In Example 2, biaxial stretching was carried out in the same process as in Example 1 except that melt extrusion was carried out from a T-die in which the entrance diameter to the die portion was 30 mmφ and the lip exit was kept at 2 mm. A film was obtained.

(Example 3) The unstretched sheet obtained in the same manner as in Example 1 was subjected to simultaneous biaxial stretching at 100 ° C. at 4.1 times in the machine direction and 4.1 times in the width direction. Stretched,
Heat treatment at 240 ° C, cool to room temperature, thickness 12μ
m biaxially stretched film was obtained.

(Example 4) A biaxially stretched film was obtained in the same manner as in Example 1 except that the blending amount of the block copolymerized polyester (B) was changed to 19 wt%.

Example 5 A biaxially stretched film was obtained in the same manner as in Example 2, except that the blending amount of the block copolymerized polyester (B) was changed to 19% by weight.

Example 6 As a crystalline polyester (A), RE553 manufactured by Toyobo Co., Ltd. (intrinsic viscosity: 0.63 dl / g)
Using 82 wt% of terephthalic acid as a dicarboxylic acid component as a block copolymer polyester B;
As a diol component, a mixture of 93.3 mol% of butanediol, 6.7 mol% of polytetramethylene glycol, 9 wt% of a polyester (reduced viscosity 1.50 dl / g), and 9 wt% of polybutylene terephthalate were simultaneously mixed with pellets. Except for the above, a biaxially stretched film was obtained in the same manner as in Example 1.

Example 7 As a crystalline polyester (A), RE553 manufactured by Toyobo Co., Ltd. (intrinsic viscosity: 0.63 dl / g)
Using 82 wt% of terephthalic acid as a dicarboxylic acid component as a block copolymer polyester B;
As a diol component, a mixture of 93.3 mol% of butanediol, 6.7 mol% of polytetramethylene glycol, 9 wt% of a polyester (reduced viscosity 1.50 dl / g), and 9 wt% of polybutylene terephthalate were simultaneously mixed with pellets. Except for the above, a biaxially stretched film was obtained in the same manner as in Example 2.

(Comparative Example 3) In Example 6, biaxial stretching was carried out in the same process as in Example 1 except that melt extrusion was carried out from a T-die in which the entrance diameter to the die portion was 30 mmφ and the lip exit was kept at 2 mm. A film was obtained.

(Comparative Example 4) In Example 7, biaxial stretching was performed in the same process as in Example 1 except that the melt extruded from the T-die with the entrance diameter to the die portion being 30 mmφ and the lip exit being 2 mm. A film was obtained.

The results are shown in Table 1.

[0043]

[Table 1]

[0044]

According to the present invention, the biaxially stretched polyester film has the following characteristics: durability, moisture resistance, mechanical properties,
An improved biaxially stretched polyester film having heat resistance, oil resistance, optically and mechanically high anisotropy, and extremely high tearing straightness in the MD direction of the film is stably provided. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of evaluation of tear straightness.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B65D 85/72 B65D 85/72 Z C08J 5/18 CFD C08J 5/18 CFD C08L 67/00 C08L 67/00 // B29K 67:00 B29K 67:00 B29L 7:00 B29L 7:00 (72) Inventor Keiji Mori 344 Maehata, Kizu, Oji, Inuyama-shi, Aichi Prefecture Toyobo Co., Ltd. Inuyama Plant (72) Inventor Imai 344 Inuiyama-shi, Aichi Pref. QA02 QA03 QC05 QC06 QG01 QG18 4J002 CF061 CF073 CF102 GG02

Claims (6)

[Claims] 1. A polyester film comprising a mixture of two or more polyesters, wherein a phase obtained by a resin melt extrusion step and a subsequent stretching step in which a shear rate is sharply increased spatially and / or temporally. A biaxially oriented polyester film having a separation structure and having an isotropic evaluation value of 0.70 or less. 2. The biaxially oriented polyester film according to claim 1, wherein the biaxially oriented polyester film has excellent tear straightness in a machine flow direction. 3. A biaxially oriented polyester film, wherein the phase-separated structure according to claim 1 or 2 is a string-like island shape. 4. A mixture of the polyester according to any one of claims 1, 2 and 3, wherein 90 to 70% by weight of a crystalline polyester resin (A) containing at least 80 mol% of terephthalic acid and a crystalline segment having a melting point of at least 170 ° C. Block copolymer polyester (B) consisting of a soft polymer having a melting point or a softening point of 100 ° C. or less and a molecular weight of 400 to 8000.
An axially oriented polyester film characterized by being a mixture of 0 wt% 5. A crystalline polyester resin (A) containing at least 80 mol% of terephthalic acid, a crystalline segment having a melting point of 170 ° C. or more, and a melting point or softening point of the polyester mixture according to claim 1. Is a mixture of a block copolymer polyester (B) consisting of a soft polymer having a molecular weight of 400 to 8000 or less and a polybutylene terephthalate (C), and (A) being 90 to 7
A biaxially oriented polyester film, wherein 0 wt% and the total amount of (B) and (C) is 10 to 30 wt%. 6. A method for producing a biaxially oriented polyester, comprising a resin melt extrusion step of rapidly increasing a shear rate spatially and / or temporally, and a subsequent stretching step. A method for producing an oriented polyester film.